The present invention relates to a drive apparatus and speed control apparatus for a brushless motor to be employed for home-use equipment such as an air conditioner and a hot-water supply device.
Alternating-current electric motors (which will be referred hereinafter to as ac motors) are often utilized as a drive motor for home-use equipment such as an air conditioner and a hot-water supply device, and fan motors for use in the air conditioners and hot-water supply devices are required to be variable in speed so as to adjust the quantity of air to be blown thereby. Generally, the ac motor can be driven with a direct connection to an alternating-current power source (a commercial power source) so as to give an advantage in terms of very easy handling, while difficulty is encountered to change its rotational speed Accordingly, instead of such an ac motor, direct-current brushless motors (which will be referred hereinafter to as dc brushless motors) are frequently used however, such as motor can easily change its rotational speed. One example of drive apparatus of the conventional dc brushless motors is illustrated in FIG. 1. A description will be made hereinbelow with reference to FIG. 1 in terms of the drive apparatus of the conventional brushless motor. In FIG. 1, a position-detecting circuit 1106 is responsive to the output signal of a position sensor 1105 so as to output a position detection signal. An energization switching circuit 1107 outputs an energization switching signal for drive coils 1101a to 1101c of the motor on the basis of the position detection signal. This energization switching signal is power-amplified by means of a power circuit 1108 before successively switching the energization states of the drive coils 1101a to 1101c so as to drive the motor. A power from a commercial power source 1102 is rectified and smoothed through a rectifying and smoothing circuit 1103 so as to produce a dc voltage which in turn, drives a switching power source 1104. The switching power source 1104 varies the dc voltage to be applied to the power circuit 1108 so as to change the rotational speed of the motor.
There is a problem which arises with such an arrangement of the drive apparatus of the brushless motor, however, in that the switching power source should be required in order to change the rotational speed of the motor and a number of elements such as coils, capacitors and resistors are required for constituting the switching power source so that a number of mounting spaces are required for constituting the system which makes it difficult to simplify the system and reduce the weight and size of the system, thereby increasing the system cost.